antennas to a lot of places! Here are some of the actual test results that didn't make it into the article. We
modified the SWR sensor in one of the prototypes and reduced the power to way below 100 milliwatts to check
everything from 1.6 to 30 MHz.
A 40 meter dipole (at 30 feet) would tune anywhere from 3.1 to 30 MHz! We had some problems at 19
and 28 MHz finding a 1.5 match. The AT-11 usually found a 2.0, then we had to use the manual switches to get
below 1.5.
Next, an Antron-99 (at 40 feet) would tune anywhere from 30 to 5 MHz. The auto mode worked great
the whole time. We just dialed down the band and the AT-11 would kick in when ever the SWR went over 3.0.
Then we tried out the unit on a friends 3 element tri-band (20,15,10) at 70 feet. It would tune any of
the ham bands (including WARC) except 160 and 80. We had some problems finding a match around 27.200
MHz, but got around it by moving to 27.000, letting the AT-11 find a match, then moving back to 27.200.
The 80 meter inverted Vee was next. It tuned everything from 3.1 to 30 MHz. We were hoping that it
would tune all of 160 meters, but it only found good matches from 1.900 to 1.800 MHz.
We've tried many other antennas with similar good results. There may be a place or two that your
antenna (dipole, inverted-Vee, vertical, beam, ect.) won't tune. Also, the farther away from resonance you try
to tune, the harder time the tuner will have. The AT-11 will tune a 10 meter vertical to 80 meters, but your
performance will not be that great (you can't get something for nothing).
For balanced lines and random wires, you may get better performance by using a 4 to 1 or 6 to 1 balun
between the antenna and tuner.
We used the Autek RF-1 analyzer to give us more information about how well the AT-11 was working.
We found that it would consistently tune impedances from about 8 ohms to about 650 ohms. This corresponds to
an SWR of about 8:1 for Low-Z and 10:1 for Hi-Z.
The SWR bandwidth (usable bandwidth of 1.5 SWR without retuning) averaged about 200 kHz. On the
lower frequencies it was smaller (about 75 kHz on 80 meters) and on the higher frequencies it was larger
(about 400 KHz on 10), no surprises here.
Trouble Shooting: The AT-11 goes together very easy and the dozens of units that we have built have all
worked on the first try. If there are any problems, first check all components for proper value, placement and
polarity. Next look at the solder connections. Check for cold solder joints and solder bridges first, since they
are the number one cause of problems with the kits.
Does nothing: Check for 12 volts getting to PC board. Check for 5.0 volts out of 78L05. Make sure the
6
